1. Field of the Invention
This invention pertains to asphalt paving compositions for use in road building and the like. More particularly, this invention pertains to processes for making cold mix asphalt paving compositions containing reclaimed asphaltic pavement.
2. Background of the Related Art
Asphalt may be treated for use in paving compositions by using one of two conventional methods. These methods are appropriately called the "hot mix" and "cold mix" methods.
In the hot mix process, the asphalt is liquified at approximately 300.degree. F. to 350.degree. F. by heating. The viscosity of the asphalt decreases as the temperature increases and it becomes a liquid at a temperature sufficiently below its flash point. The melted asphalt is then mixed with aggregate. The aggregate must also be hot when it is combined with the liquid asphalt so it does not cool the asphalt and cause it to solidify. Therefore, hot mix plants incorporate a rotary kiln to dry the aggregate and heat it to a few hundred degrees Fahrenheit. The hot aggregate is then mixed with the liquid asphalt. The asphalt/aggregate mixture is stored until it can be transported.
In conventional cold mix processes, the liquid asphalt is in the form of an asphalt emulsion. The asphalt emulsion is then blended with a sized aggregate to form a cold mixture useful for asphalt pavement. The aggregate then cements into a hard pavement that is essentially identical to the hot mix bituminous asphalt.
U.S. Pat. No. 2,701,213, to Neville, teaches a process for producing an asphalt paving composition. The process comprises removing the used asphaltic material from the road surface, reducing the material in size, adding additional asphalt conditioner to the material, and curing the resulting mix. This process necessarily utilizes an asphalt conditioner having at least forty percent by weight of aromatic hydrocarbons.
U.S. Pat. No. 4,946,307 describes an apparatus for the cold, in-place recycling of asphalt paving of an asphalt roadway. The apparatus includes a cylindrical milling drum which serves to remove a thickness of the asphalt paving and break the same into particles as the apparatus moves forwardly along the roadway. The particles are lifted to a separating drum which separates the particles according to size. The relatively small particles are mixed with a suitable liquid additive and then discharged onto the roadway. A following paver then forms the discharged material into new paving. The oversized particles are discharged onto the roadway at a location in front of the milling drum.
In all of the prior art, asphalt pavement recycling processes, existing asphalt pavement is ground and immediately passed into a reconditioning process.
None of the prior art processes are applicable to the recycling of asphalt rubble that contains impurities such as dirt. Often when asphalt pavement is removed from the ground there is a large amount of dirt accompanying the broken, excavated asphalt rubble. Presently all such asphalt rubble is disposed by dumping it into a landfill. Due to the preciousness of available landfill space it is highly desirable, if not governmentally mandated, to recycle as much asphalt pavement as possible. It is also highly desirable to recondition asphalt with a conditioner having less than 20% of aromatic hydrocarbons to conform with air quality standards.
It is also desirable to provide a centralized asphalt reclamation site to which excavated asphalt rubble can be transported and dumped for recycling.
It is therefore an object of the present invention to provide a process to separate impurities from asphalt rubble and to process the separated asphalt rubble into a cold mix asphalt pavement.
It is a further object of the present invention to provide a cold mix asphalt pavement having a low amount of aromatic hydrocarbons in the added asphalt binder.